Hi Gosouth,
Many good comments and questions which only the company could answer - but can't at the moment for the most part for Jorc reasons. Some speculations from me.
After posting about the R&P mining method I re-read it and had thought about Block caving, long hole stoping, continuous miners for coal etc which would likely be
cheaper per unit of ore.
The upfront cost of these can be an order or more of magnitude greater than the suspected cost of Opasura (say $50M). They need orebodies of a scale to warrant such extraction methods - NCM Cadia area; Rio/BHP Resolution, Arizona (~$2B); Carrapateena OZL (~$0.8B) etc with the latter two in the development stage. Doubt if this would surprise you but others may find it interesting.
The mining method as you suggest needs an appropriate orebody - size,configuration,
geotechnical etc.
At a meeting TR said he would be happy to conduct the meeting inside the adits of 40 year old workings at Opasura because they were still standing and safe = probable good strong geotechnical characteristics. Obviously much more study would be needed but sounded like a good start.
Why are they charging ahead with a scoping study? Speculations:
The
updated presentation of 9/11/2017 gives the following time line ONLY 2 months after acquisition:
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Many implications to this:
Opasura filled many attributes to be AZS's
Flagship post Teck clawback at Alacran.
To make this tight? schedule suggests a fair deal of confidence in historical work IMO.
Since then the mineral resource has supported the exploration target, at least for tons.
The geology with most of the known mineralisation in the Arenillas Formation has largely been explored for obvious near surface mining potential at least to inferred/indicated level with some 7-9 years of resource at 1000 tpd outlined.
While a larger resource would be better AZS has to prioritise funds and probably produce REVENUE (Soothsayer's wish) in a reasonable period of time. Another 3-6 months or more of exploration/definition drilling would likely require another capital raising which the market would not take too kindly to IMO.
Another thing the market detests is missed goals without adequate reasons. AZS had better meet the November 2017 (and subsequent announcements) self imposed goal of a PEA by the end of Q3 2018. (Note "underway in Nov 2017!".)
Significant Phase 2 drilling will be done concurrently with the studies and feed into any DFS that may result.
My sectional work shows, to me (a
NON resource geo), that more detail is likely to be required between Phase 1 drill density to enable a definitive mine plan.
As with such infill drilling it is likely there will be swings and roundabouts where thickness, grades and continuity will be different than predicted from phase 1 and historical work. Overall the final result may be similar in quantity if not detail to the current mineral resource.
There are likely to be some extensional drill holes as well.
startling above about the tight schedule and there are likely to be other factors.
Geophysics?
As I have mentioned before I am a geo with a career that has peripherally involved geophysical surveys/data so DYOR on what is below.
The relatively flat lying nature of known mineralisation at Opasura could require careful consideration in the choice of geophysical technique.
Topography looks quite rugged but should be manageable for most survey types.
Prioritising budgets? Geophysics vs drilling and SS/PEA etc - $s
Electrical techniques - simple ones EM/IP??
The main zinc mineral is sphalerite which has generally poor electromagnetic (EM) properties so is rarely the primary target for this style of geophysics. Not certain about galena (lead sulphide) but suspect it isn't great either.
So for many replacement style/VMS base metal sulphide deposits it is associated minerals such as pyrite, pyrrhotite and, less commonly, magnetite that are detected by EM, IP, or Magnetic surveys. That means there may not be a correlation between economic minerals and anomalies picked up by a surveys.
Having said that anomalies in an appropriate stratigraphic position at a known deposit such as Opasura have a reasonable chance of being base metal rich.
[Recent drilling at Sara Alicia may be a case in point. A strong magnetic anomaly was reported but drilling
to date ?shows a "plunging shoot" rather than a large planar Au/Co enriched feature (especially holes 11-13). Early days but IMO one of the reasons AZS has a for sale sign on SA. I suspect it might be a different case if they had a guarantee to get the surrounding land that is currently tied up in the Tenement ?backlog/etc. S's??? a problem as well?]
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Gravity could be quite interesting given the probable strong density contrast of massive sulphides to host lithologies.
Drilling to date shows mineralisation is partly structurally controlled as well as stratigraphically. Gravity could define areas of high and low sulphides for targeted drilling.
Seismic? possible - cost? topography? sufficient definition???
Another thought on the lack of use on geophysics is that historical drilling + other previous work may provide enough of a framework that the cost of such surveys are better spent in drilling phase 2 at this stage. Again budget/money....
If studies show a mine is possible I imagine geophysics will play a role both for Arenillas style replacement mineralisation relatively close to surface and deeper targets.
In due course IP surveys may be conducted at Opasura to see if there is a deep heat system that has driven the near surface mineralisation. Porphyry style?? as hinted at by AZS by the presence of mineralisation in Revancha (minor) Arenillas (dominant) and Candelaria (minor) stratigraphic levels.
A little mentioned deposit exists east of Opasura - Candelaria (Ag) which IMO may be a good IP target. Back burner for the moment.
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